The present invention relates to an image display device and a light emission device, more particularly to an image display device of a small size with high performance and high reliability and a light emission device which is suitable for various kinds of uses including a light source of the image display device.
An image display device plays a role as an interface that visually connect various kinds of electrical equipment and human beings. In the present information society, the role of image display devices is essential, and the image display device is a key component in a wide field that includes television sets, computers, information terminals, game machines and household electronic appliances. At the same time, development of new high performance image display devices is desired to meet the needs of the present information society as it rapidly develops and increases in diversity.
For such image displaying devices, a Braun tube and a liquid crystal display device have been mainly used. The Braun tube scans an electron beam in a glass tube sealed to produce a vacuum and excites fluorescent bodies arranged on a shadow mask, thereby displaying an image. The Braun tube can be manufactured relatively low in cost, and is capable of displaying high quality images. Therefore, in general, the Braun tube is widely used as an image display device for television sets, computer monitors, etc.
On the other hand, a liquid crystal display device applies a designated electric field to a liquid crystal layer held between two substrates, thereby changing an optical property of the liquid crystal layer to display changes of intensities of transmitted light and reflected light in the form of a predetermined image. When the liquid crystal display device is compared with the Braun tube, the liquid crystal display device has an advantage that it is thin in thickness and light in weight. Liquid crystal display devices are used in electronic equipment such as notebook computers and various kinds of portable information console units.
With the development of the foregoing electronic equipment and the advancement of the information society, image display devices must be made smaller in size, lighter in weight, and display an image with higher quality and reliability.
However, the Braun tube has structural problems because it is large in length in its tube direction, heavy in weight, and since it is a vacuum glass tube, it has an insufficient durability against vibrations and shocks.
On the other hand, a conventional liquid crystal display device uses a cathode fluorescent tube as its light source, which meets manufacturers needs for a small-sized, thin cathode fluorescent tube having long life, in addition to having display luminance. However, there is a problem in liquid crystal display devices, that the visual field angle is narrower than that of the Braun tube, so that image recognition from an oblique direction is significantly poor.
The present invention was made from the viewpoint of the above described circumstances. Specifically, the object of the present invention is to provide an image display device which is easy to manufacture, small in size, light in weight, having has a wide visual filed angle, capable of displaying a high quality image, and having a high reliability, and to provide a light emission device which is suitably used for a light source of such image display device and for other various kinds of uses.
Accordingly, one object of the present invention is to provide a novel image display device that comprises a light source section which includes a semiconductor light emitting element as a light source, a light adjustment section which adjusts an intensity of a light emitted from the light source section for each of pixels, and transmits the pixels as a transmission light. The image display device also includes a wavelength change section which receives the transmission light transmitted from the light adjustment section and emits light having an intensity spectrum different from that of the transmission light.
The light adjustment section in the image display device adjusts the intensity of the transmission light by a liquid crystal cell, and the wavelength change section comprises a phosphor.
The semiconductor light emitting element of the light source section is the one which emits a light exhibiting a light emission spectrum having a peak wavelength in a ultraviolet region. The wavelength change section comprises three kinds of phosphors arranged according to a predetermined pixel pattern. The three kinds of the phosphors are the ones which convert the said transmission light into visible rays of lights of red, green and blue wavelength zones, respectively, whereby the image display device can display a clear and bright image with a low power consumption.
Moreover, the semiconductor light emitting element comprises a gallium nitride type semiconductor as a light emitting layer, in which a peak wavelength of a light emission spectrum is set to be at a range of 360 nanometer to 380 nanometer. The wavelength change section uses a phosphor exhibiting an absorption excitation peak in a wavelength region which is substantially the same as that of the said peak wavelength of the foregoing phosphors, whereby an image display device of a high efficiency can be provided.
Moreover, a light transmitting substrate of the light adjustment section is formed of a low alkali glass, a no-alkali glass or a quartz glass, whereby the absorption of a ultra violet ray is reduced so that a luminance is increased.
Moreover, by providing an ultra violet absorption filter in the wavelength change section, it is possible to suppress the entry of a ultra violet ray from the outside as well as the leakage of a ultra violet ray emitted from the semiconductor light emitting element to the outside.
Moreover, the semiconductor light emitting element exhibits a light emission spectrum, in which the peak wavelength is at a blue range. The wavelength conversion section comprises two kinds of phosphors and one kind of filters, arranged according to a predetermined pixel pattern. The two kinds of phosphors are organic phosphors which convert the foregoing transmission light to a visual light in a wavelength zone such as red or green zone and one kind of filter transmit the foregoing transmission light, so that the image display device with a high efficiency can be provided.
On the other hand, the image display of the present invention may be alternatively constituted in such a manner that a light source section including a semiconductor light emitting element as a light source, a wavelength change section which receives light emitted from the semiconductor light emitting element and emits a light exhibiting a different intensity spectrum from that of the received light, and a light adjustment section which adjusts the intensity of the light emitted from said wavelength change section, corresponding to each pixel of an image to be displayed, and transmits it as a transmission light.
Moreover, the semiconductor light emitting element as the light source of the image display device emits a light exhibiting a light emission spectrum, a peak wavelength of which is in an ultraviolet ray range, and the phosphors convert the lights emitted from the said light conduction plate to visible lights having respective peaks in wavelengths zones of red, green and blue thereof.
Moreover, the light adjustment section comprises either a guest-host type liquid crystal or a high polymer diversion type liquid crystal. To keep balance of luminance for every color, the pixel pattern has different pixel area depending on each color, and the light source sections may be constructed in various types, whereby it will make it possible to display a clear image with a high efficiency.
Moreover, the image display device of the present invention comprises a light source section having a semiconductor light emitting element and a movable reflection mirror in the light source section, and a wavelength change section which receives a light emitted from said light source section to emit it after changing its intensity spectrum, wherein the light from the semiconductor light emitting element is reflected by moving the movable reflection mirror and the reflected light is incident onto a predetermined position of said wavelength change section.
Moreover, the image display device of the present invention may comprise a variable lens instead of the movable reflection mirror.
On the other hand, the light emitting element of the present invention comprises a light emitting diode which includes a gallium nitride type compound semiconductor as a light emitting layer and a phosphor which is deposited in at least one portion of a surface of the light emitting diode, wherein the light emitted from the light emitting diode is subjected to a wavelength change by said phosphor and is emitted to an outside of the light emitting diode.
Moreover, the light emitting element of the present invention comprises a mounting material, the light emitting diode which includes a gallium nitride type compound semiconductor as a light emitting layer mounted on the mounting material, and resin molding the light emitting diode, wherein a phosphor is deposited on a surface of the resin and the light emitted from the light emitting diode is subjected to a wavelength change by the phosphor and is emitted to the outside.
Alternatively, the light emitting element of the present invention comprises a mounting member, the light emitting diode mounted on the mounting member, and resin which molds the light emitting diode, wherein said mounting member comprises a reflection plate provided around the mounting member of the light emitting diode and a phosphor deposited on a surface of the reflection plate, and wherein a light emitted from the light emitting diode is subjected to a wavelength change by the phosphor and is emitted to the outside.
Alternatively, the light emitting element of the present invention comprises a light transmission substrate, a layer formed of a phosphor stacked on the light transmission substrate, and a light emitting diode which includes a gallium nitride type compound semiconductor as a light emitting layer, being mounted on the phosphor layer, wherein a light emitted from the light emitting diode is subjected to a wavelength change by the phosphor layer, and is emitted to the outside after transmitting through the light transmission substrate.
Or, the light emitting element of the present invention comprises a light emitting diode having a multi-layered structure composed of a plurality of semiconductor layers including at least one gallium nitride type compound semiconductor, wherein at least one of said semiconductor layers includes a phosphor which performs a wavelength change for a light emitted from said light emitting diode and emits it to the outside.
Or, the light emitting element of the present invention comprises a plurality of light emitting diodes, each of which emits a light of a wavelength different from those emitted from other light emitting diodes and is stacked so as not to shade the light emitted from other diodes when viewed from a light exiting direction, wherein the light emitted from each of the light emitting diodes can be taken from the light exiting direction.
According to the present invention, it is possible to provide an image display device which is capable of displaying an image with a very wide visual field angle compared to an ordinary liquid crystal display device, the image being recognized clearly even when viewed obliquely.
According to the present invention, it is possible to provide an image display device which is capable of displaying a distinctive image without blur and vagueness.
According to the present invention, since in the image display device of the present invention the light source section employs the semiconductor light emitting element as a light source, the image display device can exhibit an extremely high photoelectric conversion efficiency and has an ability to reduce power consumption compared to the conventional image display device such as the liquid crystal display device.
According to the present invention, the image display device of the present invention employs the semiconductor light emitting element as a light source, whereby a high photoelectric conversion efficiency can be achieved and the power consumption can be reduced compared to the conventional cathode fluorescent tube. For example, the power consumption of a 10.4 inch type thin film transistor (TFT) liquid crystal display device using the conventional cathode fluorescent tube as a light source is about 9 watts. On the contrary, the power consumption of the image display device adopting an ultra violet LED and the phosphor is about 4 watts, specifically, the power consumption is reduced to be less than half of that of the conventional liquid crystal display device. As a result, battery life of portable electronic equipment such as a notebook type computer and various kinds of information portable console units which incorporate the image display device of the present invention can be prolonged.
Moreover, according to the present invention, in the light source section of the image display device, the circuit thereof is simplified compared to the conventional cathode fluorescent tube, where the driving voltage for the light source section can be reduced. Specifically, the conventional cathode fluorescent tube had to be applied with a high voltage via a stabilizing circuit or an inverter. However, according to the present invention, the semiconductor light emitting element serving as a light source has an ability to provide a sufficient light emission intensity with a DC voltage as low as 2 to 3.5 volts. Therefore, there is no need of a stabilizing circuit or an inverter circuit for the semiconductor light emitting element, so that the driving circuit for the light source is greatly simplified and the driving voltage for driving the light source can be reduced.
Moreover, according to the present invention, the life time of the light source incorporated in the image display device can be significantly prolonged than that of the conventional image display device. Specifically, in a conventional cathode fluorescent tube, luminance is rapidly lowered after the passage of a predetermined life time period due to sputtering phenomenon at the light source section, and light emission stops. According to the present invention, reduced luminance is rarely found even when the light source has been used for an extremely long time as long as several tens of thousands of hours, and the life time of the light source can be said to be quasi-permanent.
Moreover, the image display device of the present invention has a very short rise-up time for the light emission. Specifically, the period of time from a signal input for starting of driving to a stationary state in the light emission is very short compared to the conventional cathode fluorescent tube so that the image display device of the present invention is capable of starting an operation instantaneously.
According to the present invention, the reliability of the image display device of the present invention can be increased. Specifically, the conventional cathode fluorescent tube has a structure that seals a specified gas in a glass tube. Therefore, in some cases, the cathode fluorescent tube is broken by excessive shock and vibration. According to the present invention, however, since the semiconductor light emitting element that is a solid state element is used as a light source, reliability against shock and vibration increases remarkably.
Moreover, according to the present invention, there is no need of harmful mercury. Specifically, in the conventional cathode fluorescent tube, a designated amount of mercury is often sealed in its glass tube. The image display device of the present invention need not use such harmful mercury.
Moreover, the light emitting element of the present invention is small in size, thin in thickness, and exhibits high luminance and is reliable. A plurality of emitted lights having different wavelengths such as red, green and blue colors can be simultaneously produced from the light emitting element of the present invention. As described above, according to the present invention, provided are the image display device and the light emitting element which have simple constitutions and are small in size with a high reliability. In addition, excellent industrial advantages, including those described above and hereinafter, can be brought about by the present invention.